A number of precision fluid metering applications, such as micro-pneumatic and fuel injection systems, as non-limiting examples, employ solenoid-driven actuators to control fluid flow through a fluid supply valve. Optimally, fluid flow through the valve is to be maintained very closely in proportion to the current applied to the solenoid. However, varying fluid pressure conditions at the valve's inlet and/or outlet ports can significantly impact the ability of the solenoid to provide the precise metering control desired.
In order to deal with this problem, it is common practice to incorporate into the valve a pressure balancing sub-assembly, such as a dual diaphragm-based pressure-balancing mechanism of the type diagrammatically shown in cross-section in FIG. 1. This dual diaphragm mechanism serves to compensate or effectively ‘balance’ out the fluid pressures at each of its inlet and outlet ports such that that the only translation forces acting on the valve orifice-closing poppet will be those imparted by the solenoid-driven armature.
More particularly, in the example valve architecture of FIG. 1, compensation for the fluid inlet pressure P1 of a fluid applied to a valve inlet port 11 of a solenoid-operated fluid valve 10 is provided by ‘upper’ diaphragm 21, installed between armature-poppet connecting rod 23 and solenoid actuator assembly 25. The upper end of armature-poppet connecting rod 23 engages moveable armature 24 of the solenoid actuator, while the lower of armature-poppet connecting rod 23 engages poppet 27, which is sized to be flush against valve seat 31 surrounding valve orifice 33. Valve orifice 33 provides fluid communication between fluid cavity 35, to which fluid inlet pressure P1 at valve inlet port 11 is applied, and fluid exit port 37 from which fluid outlet pressure P2 is derived.
By making the annular area AD1 of ‘upper’ diaphragm 21 substantially the same as or very close to that of the area AO of orifice 33, the downward force (as viewed in FIG. 1) imparted by the fluid inlet pressure P1 against poppet 27 will be substantially the same as, or performance-wise sufficiently close to, the ‘upward’ force imparted by the fluid inlet pressure P1 against upper diaphragm 21, thereby effectively neutralizing the contribution of the fluid inlet pressure P1 to the position of poppet 27 relative to the valve seat 31.
In a complementary manner, compensation for fluid outlet pressure P2 at fluid exit port 37 is provided by ‘lower’ diaphragm 41, installed between lower end 43 of poppet-connecting rod 45 and valve body 47. Upper end 51 of poppet-connecting rod 45 engages poppet 27. Similar to the compensation mechanism for fluid inlet pressure P1, the annular area AD2 of ‘lower’ diaphragm 41 is made substantially the same as or very close to that of the area AO of valve orifice 33.
As a consequence, any upward force imparted by fluid outlet pressure P2 against poppet 27, which might otherwise tend to lift poppet 27 off of valve seat 31 (and thereby undesirably render solenoid control ineffective), will be countered by a ‘downward’ force imparted by fluid outlet pressure P2 against lower diaphragm 41, so as to effectively neutralize the contribution of fluid outlet pressure P2 to the position of poppet 27 relative to valve seat 31.
Although a dual diaphragm-based pressure compensation structure of the type shown in FIG. 1 is effective for its intended purpose, it is hardware intensive in terms of the added diaphragm, connecting rods, and increased sized and additional boring of the valve body proper. This added hardware complexity not only increases the size of the assembly, but the cost and complexity of its manufacture.